Mini Diamond Theremin Speaker

Hi all, I just threw together a little mini diamond theremin speaker over the last couple of days. I used a picture frame someone chucked in the bin, and the soundboard from an old amp, along with a brand new Jensen speaker.

The diamond speaker measures 16 inches, tip to tip, and is mounted on a standard mic stand.

Here's a link to the pics of the "nearly completed" project. Just have a few touch-ups left to take care of.

I had tossed around the idea of using a picture frame as a moulding as well. The problem I see is that it would need to be very understated so it didn't LOOK like a picture frame with a very boring (or blank) picture.

Have you completed the large speaker yet? I don't recall seeing you post any pictures of the final details.

What I'd like to know is...how do they sound?Are you happy with the results and how would you describe the sound?

Hi Jeff, I agree, there needs to be interesting details within the frame, and not just a boring looking soundboard. I still have some of the reflective holo film lift over, and I've been debating the idea of using it on the mini diamond like I did on the grand speaker. It does have speaker cloth on it which is the same color as the soundboard, and unfortunately that does not show up well in the pics.

As far as sound goes, I'm very pleased with the sound of the grand speaker. Naturally, the smaller soundboard of the mini does not have quite as much richness as the grand. However, it works more like the way Coalport likes his speakers. It's more of a soprano than a baritone. Both sound good enough to use in public.

The grand is not quite complete. I'm waiting on a custom ordered set of ornaments for the corners. Once those are here, the grand diamond will be completed.

As someone who has built speaker boxes in the past, I can't help but notice that your designs are not baffled.

As any speaker DIY-er can attest, a "speaker" is really a system, consisting of a driver (the part people tend to call a "speaker"), a crossover (if applicable) and a baffle (i.e. the box in which the driver is mounted.) A driver alone is terribly inefficient, since the air around it is being filled with both positive and negative-going waveforms - the air is being pushed in one direction from the front and the other (equal and opposite) direction from the rear. These waves tend to spill out on their opposite sides, and reflect off of surfaces in the room, so phase cancellation is a big problem.

The very simplest speaker box design is an "open back" baffle, which is the common way of doing it with guitar amps. The sides of the box tend to keep the waves coming out of the rear from mixing with the ones coming out of the front. The drawback is a lack of bass response, so you don't see this used on bass amps. On electric guitars, the bass response isn't very low anyway so it doesn't really matter.

Early hi-fi speaker designs used a "horn baffle" design which sent the rear waves through a complex chamber of reflecting surfaces that acoustically flipped the phase of the waves by the time they exited the front of the speaker box. The drawback was that these boxes are typically huge, since the exit had to be large enough to accommodate the lowest waves, so the hole was usually as big as the driver, at least. Another way was to use a "passive radiator" which was in effect a driver with no power, that was pushed by the rear waves as they bounced off the rear of the baffle box, resulting in a (mostly) in-phase combination.

But both systems take up lots of space. Consumers wanted smaller boxes they could put on a shelf.

The simplest way to deal with the problem (and the main design of bookshelf speakers through the early 1960s) was the "infinite baffle", which basically was a heavy sealed box filled with some kind of dampening material like fiberglass fuzz or foam rubber to kill the rear waves. That way only the front-firing waves are heard. But this decreases efficiency of the speaker by at least half (only half of the power generated is going to make sound waves.)

Then two Aussies named A. Neville Thiele and Richard H. Small came up with means to calculate the resonant frequency of a speaker cone, and a formula match it to an "exit hole" in the front, with a tube attached that reaches toward the rear of the box. The "Thiele-Small parameters" of a speaker driver determine the size of the box, diameter of the hole, and the depth of the tube needed to result in phase-coherent waves and flat response in the front for a given size and mass of driver.

I've never seen a real RCA theremin speaker "in the flesh", but I'm guessing by the vintage that they were open-back designs, which nearly everything was in those days. I don't know how deep the sides were, but they were definitely there. They were not simply a driver mounted to a flat baffle board hanging from a stand. I can't help but think you're canceling certain frequencies and boosting others through the frequency range by not having sides on your speaker mounting boards. In practical terms, that means certain frequencies will be perceived as louder than others due to phase cancellation effects, especially toward the lower end of the scale. Do you notice any problem like this?

I understand everything you just said, and it makes perfect sense. However, there is one thing you're fogetting. The speaker design I'm using, both, are used in a corner. This seems to stop a lot of the cancellation you mentioned. Also, the size of the soundboard plays a massive roll, not just in terms of being a resonator, but I believe it's size also helps prevent "some" of the cancellation or destructive wave interferance between front and rear wavefronts.

The mini, with it's much smaller diamond, certainly is volnerable to the frequency cancellation, particularly in the low end of the frequency range, and I've considered putting an open babble on it's soundboard. As long as it's parked in the corner, it works better, but out in the open, it does struggle to provide richer lows. It does, however sound quite nice in the mid to upper ranges.

By the way, The RCA style replica of a diamond speaker as shown in stout theremin demo video does not have an open back baffle at all. It only has the speaker mounted to a very large soundboard.

Coalport, if you're reading this, you've got one or two actual vintage diamond speakers, do yours have the baffle on the back of the soundboard, or not?

When you put your speaker in the corner (assuming hard surfaces) the corner is acting as a folden horn baffle - kind of having the corner itself work as big, room-sized "speaker horn". Some old hi-fi speakers used to use the room that way, like Klipcsh "Klipschorns" or Tannoy Grenadiers. Big monsters. My uncle used to have a Klipschorn to go with his Heath valve hi-fi equipment.

I found this picture (http://etherboxspeakers.com/speakersidelarge.html) from "etherbox speakers", supposedly a re-creation of the originals.

There's clearly a box built behind the diamond baffle board, could be an infinite baffle box or an open back. A neat way of handling the problem without making a HUGE box with sides!

He mentions you on his website, so you must be acquainted with the maker, yes?

Here's a pic (http://farm2.static.flickr.com/1373/985456849_e0a65249f2.jpg) of Jen Hammaker(?) with an old RCA. I can't tell if it's an original speaker, but it appears to have sides.

I'm willing to bet even the old RCA diamond speaker had some kind of small enclosure around the driver itself, even if the diamond front panel didn't have sides per se. I doubt a company like RCA would make a production model of a speaker system that had the driver just hanging naked out of the back. It's too exposed to damage that way, for one thing. And they knew all about the phase cancellation problems of unenclosed speakers.

Even a couple of inches of flange along the sides would help. The problem with totally a flat panel is that sound waves propagate across the surface and when they reach the end, they spread (this is called the "boundary effect.") You can observe waves in water doing this as they strike a flat surface and cascade off of the end of it. you want to direct the sound waves coming out of the rear to *only* go to the rear.

Yes, I'm familiar with etherbox. Until financial disaster struck here, I was about to buy one of his speakers. Now I have to build my own if I want one.

I did notice the box on his.

Unfortunately, the link for Hemaker did not work. Let me know when the link is working. I want to have a look at that pic.

When funds become available, I do intend to add the baffle to the mini. The current grand speaker is intended for in studio use, so I'm not too worried about it's speaker just now.

If I'm ever able to build another grand speaker, yes, it will at least have the short baffle you mention, as that one will be a tour friendly design. At the moment, I've reached a reluctant stopping point for my speaker projects until funds become available.